1. Field of the Invention
The present invention relates to a method of assigning an audio channel identification (ID) by which it is possible to follow up and select the audio channel selected by a user even when a program or an audio data stream is changed in an audio/video (A/V) device for reproducing a program including a plurality of audio data streams, a method of selecting an audio channel using the same, and an optical recording and reproducing apparatus suitable therefor.
2. Description of the Related Art
Currently, a moving picture expert group (MPEG) and AC3 are often used as methods for compressively encoding an audio signal. In a linear pulse code modulation (PCM), the audio signal is not compressively encoded but recorded as it is. In digital TV broadcasting or video CDS and digital video disks (DVDs) which are digital A/V devices, the MPEG format is mainly used.
When the encoded data streams of MPEG A/V data and other data streams are integrated and applied to a real application, it is necessary to make a data stream by integrating these data streams. Auxiliary data can be additionally used according to a certain application. The role of the MPEG system is synchronizing and multiplexing video and audio data.
In the MPEG system, multiplexing by packets is adopted. In the multiplexing by the packets, each of the video and audio data is divided into data streams called packets having an appropriate length, information such as headers are attached to the packets, and the packets of the video and audio data are multiplexed.
The packets include information for identifying whether the data items are video or audio data in a region called a packet header as shown in FIG. 1. The length of the packet depends on a transmission medium or application.
Table 1 is for showing the contents of the packet headers shown in FIG. 1.
TABLE 1Main itemsPacket_start_code_prefix“00 00 01” hstream_id1 byte, for distinguishingkinds of data itemsPTS value(DTS value)DataVideo data, MPEG audiodata or private data
In Table 1, Packet_start_code_prefix represents the start of a packet and stream13 id represents kinds of data items in a packet. For example, in the case of video data, stream_id is a binary code “1110 0000”b. In the case of audio data, stream_id is a binary code “1100 0***”b. Here, *** shows that eight kinds of audio data streams can exist from 000b to 111b. In the MPEG system, other data items besides the two data items are classified as private streams. A code “1011 1101”b can be used for the private stream.
A presentation time stamp (PTS) and a decoding time stamp (DTS), defined in the MPEG system standard, respectively represent time taken to output and decode a presentation unit in the video or audio data. The presentation unit is a frame of a picture in the video data and a frame of audio in the audio data. The DTS is not necessary in the case of the audio data.
Except for MPEG audio data, audio data such as AC3 or LPCM is realized by private streams. The contents of the packet header adopted to the private streams is shown in Table 2.
TABLE 2Main itemsPacket_start_code_prefix“00 00 01” hstream_id“1011 1101” bPTS valuesubstream_idAC3 or LPCMnumber_of_audio_channelsNumber of audio channelsData
In the Table 2, the substream_id is used in order to distinguish the kinds of audio data encoding such as AC3 or LPCM. For example, in the case of the AC3, the substream_id is “1010 0***”b. Here, *** means that up to eight data streams can exist like in the MPEG audio. In the MPEG system, one program can have various video data streams and audio data streams.
The term “number_of_audio_channels” denotes the number of channels. There can be 1ch, 2ch, 3ch, 4ch, and a dual mono channel. Here, channels are different from channels selected by a user. Namely, the above channels appear as one channel to the user excluding the dual mono. The dual mono is recognized as two channels.
In an MPEG-1 or MPEG-2 program stream (PS), an upper layer of the video or audio packet, called a pack, exists. In general, a pack formed by integrating a plurality of packets is considered to be a basic unit. FIG. 2 shows the structure of the pack. Additional information for a time based reference for synchronous reproduction exists in a pack header.
Table 3 shows the contents of a pack header shown in FIG. 2.
TABLE 3Main itemsPack_start_code“00 00 01 BA” h“01”shows that data is MPEG-2SCR valueprogram_mux_ratepack_stuffing_length
In the Table 3, the Pack_start_code is a code from which pack data starts. The SCR value represents the time at which the pack data reaches the buffer of a decoder and is used for synchronizing the system clock of an encoding port with the system clock of a decoding port. The program_mux_rate represents a transmission rate at which video, audio, and private data items are multiplexed and transmitted. In order to decode data correctly, the data must be transmitted at higher than the transmission rate. The pack_stuffing_length represents the number of dummy data.
FIG. 3 schematically shows channels and audio signals corresponding thereto. As shown in FIG. 3, audio signals are output through decoders. The data of the dual mono channel having outputs, the audio data of CH0 and the audio data of CH1 is similar to the 2ch data. However, the dual mono data is different from the 2ch data in that left and right audio signals are related to each other in the 2ch data, whereas CH0 and CH1 are separate audio signals in the dual mono data.
For example, Korean language audio data can be loaded into CH0 and English language audio data can be loaded into CH1 in the dual mono channel. Therefore, in general, only one of the two channels is output or the CH0 audio data and the CH1 audio data are output through a left speaker and a right speaker, respectively.
FIG. 4 shows an example of an apparatus for decoding and outputting the data of the dual mono channel. When a select signal is 0, the apparatus shown in FIG. 4 outputs CH0 audio as left audio and right audio. When the select signal is 1, the apparatus outputs CH1 audio as left audio and right audio. When the select signal is 2, the apparatus outputs CH0 audio and CH1 audio as left audio and right audio, respectively.
FIG. 5 schematically shows a method of recording or reproducing a multi voice audio signal as dual mono audio data. The multi voice audio signal is formed of main audio data and sub-audio data. When data is recorded, the main audio data and the sub-audio data are encoded into an audio data stream through a multi-voice encoder. At this time, the main audio data is encoded into the CH0 audio data and the sub-audio data is encoded into the CH1 audio data.
When data is reproduced, an audio data stream is decoded into the CH0 audio data and the CH1 audio data through a multi-voice decoder. The CH0 audio data is main audio data and the CH1 audio data is sub-audio data.
Here, it is assumed that a plurality of audio data streams exist. As an example, when two audio data streams exist in an A/V data stream, the user can select one among the two channels. When the selected audio data stream is dual mono data, that is, sub-audio data streams are included, the user can select two channels.